Defintion $\bf 1.1.2~$ Suppose $i:A\to B$ and $p:X\to Y$ are maps in a category $\mathcal C$. Then $i$ has the left lifting property with respect to $p$ and $p$ has the right lifting property with respect to $i$ if, for every commutative diagramm $$\require{AMScd} \begin{CD} A @>{f}>> X\\ @V{i}VV @VV{p}V \\ B @>{g}>> Y \end{CD}$$ there is a lift $h:B\to Y$ such that $hi=f$ and $ph=g$.
Definition $\bf 1.1.3~$ A model structure on a category $\mathcal C$ is three subcategories of $\mathcal C$ called weak equivalences, cofibrations, and fibrations, and two functorial factorizations $(\alpha,\beta)$ and $(\gamma,\delta)$ satisfying the following properties:
- ($2$-out-of-$3$) If $f$ and $g$ are morphisms of $\mathcal C$ such that $gf$ is defined and two of $f,g$ and $gf$ are weak equivalences, then so is the third.
- (Retracts) If $f$ and $g$ are morphisms of $\mathcal C$ such that $f$ is a retract of $g$ and $g$ is a weak equivalence, cofibration, or fibration, then so is $f$.
- (Lifting) Define a map to be a trivial cofibration if it is both a cofibration and a weak equivalence. Similarly, define a map to be a trivial fibration if it is both a fibration and a weak equivalence. Then trivial cofibrations have the left lifting property with respect to fibrations, and cofibrations have the right lifting property with respect to trivial fibrations.
- (Factorization) For any morphism $f$, $\alpha(f)$ is a cofibration, $\beta(f)$ is a trivial fibration, $\gamma(f)$ is a trivial cofibration, and $\delta(f)$ is a fibration
I do not understand the definition $1.1.3.(3)$ in the snippet above:
Does it say that if $f$ has l.l.p. w.r.t. $p$ and $f$ is a trivial cofibration then
$p$ is a fibration OR that if $f$ is a trivial cofibration and $p$ is a fibration
then $f$ has l.l.p. w.r.t. $p$ ?
It says: Let $f:X'\rightarrow X'$ be a map and $C$ a class of maps suppose that for every element $Y\rightarrow Y'$, of $C$ if there exists a commutative diagram
$$\require{AMScd} \begin{CD} X @>>> Y\\ @V{f}VV @VV{c}V \\ X' @>>> Y' \end{CD}$$
then there exists a map $X'\rightarrow Y$ which make the triangles commute. Then we say that $f$ has the letf lifting property in respect of the family $C$.
Now take $C$ be the class of cofibrations, we obtain that $f$ a trivial fibration. If $C$ is the class of trivial cofibrations we obtain that $f$ is a fibration.